About 600,000 H&R Block customers face lengthy delays for tax refunds after a filing error by the Kansas City, Mo.-based tax preparer, the Internal Revenue Service said late Tuesday.

The filing blunder affects customers -- mainly students -- who filed Form 8863 for education credits. Many were upset the delay would affect applications for federal financial aid for college.

"The IRS is continuing to review the situation and working with affected software companies to assist in the processing of these tax returns," said IRS spokeswoman Michelle Eldridge, in a statement.

The IRS said the review process for affected tax returns could take as long as eight weeks. The blunder affects roughly 10% of all tax returns filing for the education credit.

Irate customers have posted angry posts to H&R Block's Facebook page. Many demanded their filing fees be reimbursed and pledged to never use the services of the tax preparer again.

"Thank you for over 18 years of service, but this will be our last tax year together," one woman wrote after detailing financial difficulties the delayed refund has caused her and her family.

The tax preparing company said it is working with the IRS to expedite the affected tax returns.

"We apologize for the inconvenience this has caused and we're glad to hear some clients are already seeing their refund status change due to work with the IRS," the company posted Tuesday on its Facebook page.